The present invention relates to internal combustion engines and more particularly but not exclusively to internal combustion piston engines.
It has been found by laboratory experiments that with conventional (i.e. non-vaporised carburation) reciprocation internal combustion engines do not even closely approximate the Otto cycle which is the usual theoretical approximation applied to internal combustion engines. This discrepancy is associated with the lengthy period necessary for combustion with the fuel in a liquid state. Usually the flame front associated with such conventional engines only exists for 30.degree. to 50.degree. of rotation of the crank shaft of the engine at normal operating speeds, while combustion still continues for approximately 150.degree. and yet there is still 25% of the fuel still unburnt or partly burnt. Present engines are not an accurate approximation of the Otto cycle, since:
1. Without "instantaneous" combustion, the high pre-expansion pressure and temperature is not reached, thus preventing an adiabatic expansion,
2. The combustion process continues during the pistons down stroke, thus releasing heat. Much of this heat is transferred to the cylinder walls, and as the piston advances towards the bottom of its stroke, an increasing proportion of the heat of combustion becomes waste heat passing through to the exhaust of the engine,
3. There is a substantial loss caused by unburnt and partly burnt fuel.
Still further to the above, high efficiencies are not achievable with conventional engines, since the fuel is not in a vaporised form and accordingly misfiring will occur when air to petrol ratios exceed 20:1.
U.S. Pat. No. 4,137,779 has proposed a solution to the above problems by providing a fuel system wherein the fuel in the petrol tank of a vehicle is heated by the engine coolant. Air is subsequently drawn through the fuel tank to be mixed with the vaporised fuel to provide an air/fuel mixture for the engine. It is a particular disadvantage of this arrangement that the petrol does not remain in a vaporised state, and accordingly condensation occurs on the interior of the conduits leading to the engine. Still further disadvantages are that the fuel to air ratio cannot be accurately controlled and starting and cold running of the vehicle is difficult due to the large volume of petrol to be heated in order to provide sufficient supply of vapor.